MultiFunction Precision Monitor
MPM-3

The Selectronics MPM-1 system is designed to provide remote display of the liquid level in a tank with exceptional precision and extreme immunity to magnetic, electromagnetic and electrostatic interference. Also, the robustness of the system allows for rugged-duty set-up and transportation especially suited for portable use.

The MPM-1 system employs a unique and proprietary method of detecting the level of the liquid in the tank. The LEVEL DETECTION TRANSMITTER unit (LDT) fires a micro-power, extremely short-duration, electrical impulse that travels from the LDT through the PCC (cable) to the LSP (probe).

This impulse travels at the speed of light all the way to the bottom tip of the probe then bounces back to the LDT. At every point along its journey that it encounters a change in electrical impedance a portion of the impulse’s energy is reflected back to the LDT as a weaker impulse. The point where the probe meets the top of the liquid level is just such an impedance change. Thus, a reflection occurs at this point. The traveling speed of the original impulse and all of its reflections is a constant. Therefore the distance between the tip of the probe and the top of the liquid is simply a matter of the timing difference between the arrivals of those two reflected impulses back at the LDT.

The LDT makes a calculation based on the parameters that have been programmed into it such as length of the probe and the distance from the tip of the probe to the floor of the tank (Offset). This calculation determines the level of the liquid with extreme accuracy. This value is then converted to the desired engineering units such as centimeters, inches, gallons, or percent. The value of this quantitative measurement is then coded into light pulses, which are fed into end of the Fiber Optic Cable (FOC) that is plugged into the LDT.

The light pulses travel through the plastic, electrically non-conductive, fiber optic cable to the remotely located Fiber-to-Line Converter (FLC) completely immune to the presence of any radio, electrical or magnetic disturbances in the vicinity. No external force can affect the integrity of these light pulses traveling safely inside their “light conduit”. At the FLC the signal is turned into high-speed digital data and then passed on to the Optical Receiver & Display (ORD) via the short differential serial Data Coupling Cable (DCC).

The ORD detects and decodes this digital data back into the liquid level value and displays that value on the digital LED readout on the face of the ORD. If the level value exceeds the ALARM value set in the ORD then an alert tone sounds, an indicator on the face of the ORD flashes, and a signal and a relay contact closure is fed out through the Alarm Control Cable (ACC) to external equipment and indicators that can alert personnel and take corrective steps.

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